The novel concepts relate to methods and apparatus for handling, reheating, storing and conveying bars or rounds, particularly those formed by continuous casting processes.
The basic production of steel includes the steps of melting the raw material, either ore or scrap; casting the melt into the desired configuration such as ingots, slabs, bars or rounds, etc.; metallurgical treatment such as reheating or soaking; fabrication such as rolling or cutting; and cooling. The finished product shipped from the steel mill will be further processed and fabricated into any of the many forms in which the metal is formed such as plate, sheet, wire, tube, rails, structural profiles, etc. The various steps involved will differ in accordance with the particular type of metal being processed and the form desired of the finished mill product. It has long been recognized that high grade metal having high quality integrity and grain structure is the result of carefully controlled casting and rolling techniques conducted at the proper temperatures.
A wide variety of metal or steel products are formed from cast bars or rounds, such bars being cast in cylindrical form having diameters ranging between 4 inches and 14 inches and in a variety of lengths. Such rounds are widely used to form seamless tube, forgings or rod for drawing wire.
Rounds may be economically cast in a continuous process by rotating casters which basically consist of a vertically oriented mold which rotates during casting, the molten metal being poured into the upper end of the caster, and the solidified cast metal leaving the caster lower end. The solidified cast metal is periodically severed to form bars or rounds of determinate length which are conveyed to subsequent treating stations. The rate at which the round is formed by the caster is determined by many variables, such as the metal composition, the diameter or cross sectional configuration of the round, the rate of metal flow into the caster upper end, and other known factors. Also, if the melting furnace capacity is not sufficient to keep the caster operation continuous the caster output will be intermittent between ladle and tundish replenishing.
As the metal flows from the caster it begins to cool and the temperature of any axial increment will be directly related to the time interval since casting. Accordingly, as the caster output is severed into lengths the resultant rounds will have a "cold" end and a "hot" end, the cold end being the forward end of the round with respect to the direction of metal movement as it leaves the caster.
It has long been appreciated that the temperature of steel must be closely regulated during cooling and processing if the optimum metallurgical characteristics are to be achieved. Overheating will "burn" the steel destroying the desired grain structure, while the rolling of steel which is too cool will produce voids, flaking and molecular slippage, and prevent a homogeneous molecular structure. Additionally, the rate of cooling, and the temperature of the steel during rolling directly effects the mallability and hardness, which are critical factors with respect to subsequent fabrication as are spread elongation ratios.
Because the continuously cast round temperature varies throughout its length and cross section the round temperature must be brought to uniformity throughout if optimum processing and metallurgical qualities are to be achieved. The rounds could be introduced into a furnace, and slowly brought to a desired uniform temperature, but such reheating is slow and wasteful as it does not efficiently take advantage of the considerable residual heat within the round resulting from the casting process.
A significant advantage of the rotary continuous casting method of forming steel rounds over prior round forming processes lies in the ability of the caster to operate in a continuous, or substantially continuous, manner wherein a steady output of bars or rounds is achieved. To most efficiently utilize this advantage of the continuous caster the processing of the rounds subsequent to casting should also be continuous, or substantially so, wherein a minimum of equipment is required to process maximum steel tonnage in a given time interval. By minimizing the duration of time between casting and rolling maximum advantage of the residual casting heat within the round can be achieved.
To the present, continuous casting processes and installations have not utilized the advantages derived from continuous casting to the utmost because of several factors. First, because continuous casting inherently produces a round having a variable temperature throughout its length and cross section reheating is necessary in order to achieve a high quality product, yet those reheating devices now being utilized do not efficiently take advantage of the round residual casting heat resulting in excessive fuel costs during the reheating stage. Secondly, as the output of the continuous caster will be considerably slower than the rate of round movement during rolling a single rolling mill is capable of handling the output of several continuous casters and yet it is not possible to accurately synchronize the output of several casters with the output of the reheating means and the rolling mill. Accordingly, in previous installations excessive time intervals would result between the rolling of sequential rounds, or excessive time durations existed between casting and reheating and known conveying and reheating structure is unable to most efficiently coordinate caster output with reheating and rolling cycles to efficiently coordinate capital expenditure with the mill capacity.